Two-stage bullet



June 1, 1965 Filed Sept. 19, 1962 A. s. HANCOCK, JR 3,186,342

TWO-STAGE BULLET 2 Sheets-Sheet l VENTO BY Za M6;

J1me 1965 A. s. HANCOCK, JR 3,186,342

TWO-STAGE BULLET Filed Sept. 19, 1962 2 Sheets-Sheet 2 I41. BERT 5 H/M/cm A.

INVENT OR.

United States This invention relates to bullets and more particularly to a two-stage bullet suitable for use in any gun having a rifled barrel.

A rifle of present manufacture using present convenventional ammunition can fire a very limited number of types of bullets. This fact severely restricts the usefulness of the gun. For instance, it is not possible to use a small bore rifle such as a .22 caliber in shooting such game as antelope or deer, and it would be absurd to try to stop African big game with such a gun. Conversely it is almost as absurd to use a large bore rifle for shooting gophers, woodchucks or other small v-armints.

By my invention 1 make possible the use of a single rifle as an all purpose gun. Thus, by my invention of a twostage bullet I make it possible for a large bore rifle to fire a small calibre bullet. Furthermore, such a bullet will have a substantially increased pert ormance characteristics.

Present bullet velocities are limited by the limitation on the possible pressures within the barrel of the gun. This is true because of the need for compromise as to the sectional density (ratio of weight to cross sectional area or to the diameter squared) of the bullet. In explanation, it will be apparent that a bullet of very low sectional densityi.e. either a low mass or a large diameter will be accelerated rapidly Within the barrel of the gun by any given pressure. However, as soon as such a bullet leaves the influence of the compressed gasses within the barrel, its resistance to the air through which it passes will be proportionately greater or its momentum will be less. Either condition will cause a loss of speed through the air. Thus it is necessary to compromise so that adequate muzzle velocity will be reached in the gun, and that sufficient of that velocity will be translated into distance and striking power after the bullet leaves the barrel.

By my invention I provide a two stage bullet having a low sectional density within the gun barrel as a first stage and a high sectional density second stage. Thus I make possible a high acceleration within the barrel and preserve the velocity outside the barrel.

Among the advantages in addition to relatively higher muzzle velocity or its complement of lower breech pressure for a given velocity are also a reduced recoil and nOise in firing a large bore gun, and a greatly increased utility of any given caliber gunparticularly those of larger caliber. As an example, there is now available a .458 caliber gun which conventionally shoots a 500 grain bullet at over 2000 feet per second. This is suflicient to kill such game as elephants, rhinoceros and the like. This gun, however, is judged to be impractical for hunting the usual North American big game such as antelope or deer and is absurd for hunting small game. This is true largely because of the very heavy recoil of the gun. However, by use of my two stage bullet having low sectional density within the barrel, I can reduce this recoil to approximately the same value as a small rifle, making the gun practical for either elephants or squirrel hunting.

Specifically, the real advantage of the two-stage bullet is in the reduction of recoil for the same striking power of the bullet, or correspondingly, the increase of striking power for the same recoil. This can be demonstrated mathematically since the recoil is a function .of momentum which is directly proportional to the product of weight and muzzle velocity of the bullet which is opposed by the weight and opposite velocity of the gun. Thus, for a gun of sufiiciently light weight to be conveniently carried, the

muzzle velocity is limited by the weight of the bullet within the limits of recoil which will be tolerated by the shooter. Since my two-stage bullet is of lighter weight, I can achieve greater muzzle velocities for the same recoil, in direct proportion to the reduction in weight. However, the striking power is measured by the kinetic energy of the bullet. This is proportional to the square of the velocity and the weight of the bullet. Therefore, a reduction in weight of /2 with a doubled velocity results in the same recoil but doubles the striking power of my bullet. Further, the fall of the bullet in its trajectory is an inverse function of its velocity and therefore the greater velocity of my bullet results in a flatter trajectory.

Further advantages of my invention, and the invention itself will be apparent from the following specifications and figures in which:

FIG. 1 is an elevational view of my composite bullet,

'FIG. 2 is a medial sectional View of the assembled bullet using a jacket second stage bullet.

FIG. 3 is a medial sectional view of the bullet using an unjacketed second stage as it arrives at the muzzle of the gun,

FIG. 4 is a medial sectional view of the bullet at the time of first stage of separation.

FIG. 5 is a view similar to FIG. 4 as the separation of the stages is completed,

FIG. 6 is a diagrammatic view to illustrate the dimensions of my bullet.

FIG. 7 is a medial sectional view of an alternate cup Which may be used in my invention.

FIG. 8 is a view similar to FIG. 7 of a second alternate cup, and

FIG. 9 is a view similar to FIG. 7 of a third alternate cup.

Briefly my invention comprises a two stage composite bullet, the first stage of which is of low sectional density and the second stage of which is of high sectional density. These two stages are properly proportioned and fitted, and are of proper comparative strength that they can be fired through the barrel of a gun as one unit, but will separate just beyond the muzzle of the gun so that the second stage may travel at a continued high velocity to the target while the first stage will fall soon after leaving the muzzle.

More particularly, and referring to the drawings, my invention comprises a bullet formed of a cup-shaped first stage it), which may also be referred to simply as the cup; and a second stage 11 which may be referred to as the bullet. As best shown in FIG. 2 the cup 10 is simply a cylindrical piece of material in which is formed a hollow 12 into which the bullet 11 is inserted. A small hole 13 may be provided for a dual purpose of easier assembly of the bullet and better separation characteristics. This stage is illustrated as having fairly sharp leading corners at 14. This type works Well, but for reasons of easier insertion of the bullet into the chambers it may be preferable to round this corner or to chamfer it.

The second stage may be a bullet of ordinary type but is preferably of a jacketed type. The jacket 20 (FIG. 2) should be relatively thicker at the base so that the bullet does not crush and expand at that region thus making separation less certain. The bullet may :be of an unjacketed type and made of an alloy such that the base does not expand on firing. The requirement is that the base of the bullet be not deformed.

The theory of the two stage idea has been briefly explained in the introduction. The principal consideration is to obtain a relatively high muzzle velocity with low breech pressures and to obtain a flat trajectory. This can be done only with two stages in which it is unnecessary to compromise between low sectional density for high acceleration in the barrel and the high sectional density for reduced air resistance in free flight. It will now be evident that all that is necessary is to provide a light weight first stage of large cross sectional area, and a heavy second stage of small cross sectional area so fixed together that they will separate at the instant the deceleration caused by air resistance starts. Obviously for accuracy, the separation must be clean and substantially instantaneous. However, as explained hereinafter, the separation of my preferred embodiment takes place in two steps which may be spaced apart in time so long as the separation is clean.

There are two possible means of causing this separation of the two stages. One would be the complete peeling off of the cup stage by a rupture. My device could Work this way. However, I prefer to use simply an expansion of the cup caused by the centrifugal force of the rotation imparted to the bullet in the barrel rifling. Rupture seldom takes place cleanly and symmetrically, and unless it does, the accuracy of the bullet is destroyed. As shown in FIGS. 3, 4 and 5, the separation permitted by centrifugal force occurs in two steps. On leaving the muzzle 17 of the gun, the walls 18 of the cup 10 expand leaving the bullet 11 free to move axially thereof. (See FIG. 4). This expansion need be very smallof the order of 1% of the diameter to relieve the holding action of the first stage on the second. For purposes of illustration, the expansion is exaggerated in the drawings. At this instant, in spite of the loose radial fit between the two stages, there is still not a complete separation since the pressure of the gasses in the gun barrel are still acting on the base of the first stage pressing it against the second stage. This has a stabilizing effect since the separation that finally takes effect is only the release of this pushing action which is a rather simple matter rather than a peeling off or the like which would take place unevenly around the bullet to throw it off course. The second step of the separation is shown in FIG. 5 as the first stage of the bullet decelerates more rapidly than the second, and the second stage begins to fly free. It is now apparent the permanent deformation of the base of the first stage 10 is to be avoided if at all possible since a deformed cup would throw the bullet 11 off course. It is also apparent that there must be no expansion at the base of the bullet 11 so that it will be completely free to move out of the cup as shown in FIG. 5.

The above discussion points up some of the problems. Other problems include the following: The strength of the first stage must be sufiicient to accelerate the first stage without shearing past it; the strength of the first stage must be sufficient to prevent stripping in the rifling of the barrel so that the bullet will receive the necessary rotative speed; the strength of the second stage must be such that it does not crush at the base to an enlarged diameter and thus interfere with the clean separation; the contact between first and second stages must be such as to impart the same rotation to the second stage as the first stage receives from the rifling of the barrel.

The mere statement of these problems, once they are recognized will lead to some of the conclusions. It will now be apparent that the material of the second stage must have a proper proportion of elasticity (so that it will expand to free the second stage), and shear strength (to provide proper rotation and acceleration of the second stage in the gun barrel). These'matters are also a function of the physical dimensions of the two stages. It will be obvious, for example that for a given outside diameter a thinner wall 18 of the cup will expand more for a given material than a thicker wall. Conversely, for a given wall thickness, the elasticity of the material must be proper The axial length L (FIG. 5) of the cup will obviously have some bearing on the shearing strength of the material chosen since this material must not shear or strip on the lands upon being forced through the barrel. Thus, the longer the cup, the less maximum shearing strength is necessary. The thickness T also is directly related to the shearing strength since the acceleration of bullet 11 reacts as a force on the base of the cup 10 tending to shear through the bottom. Thus, the cup and bullet must be properly proportioned and of only a limited range of materials.

Perhaps the first consideration should be accuracy. Therefore, the matter of proportioning the length L of the cup must be set so that it will be properly guided down the barrel and still be kept to a minimum consistent with accuracy so that the sectional density will be at a minimum.

The diameter of the first stage is fixed by the bore of the gun. The diameter B of the second stage will probably be fixed by the intended use for which the bullet is intended. The variables remaining are the thickness T and the material of the cup. The material must be chosen to have a certain elasticity to allow the expansion of the cup to free the bullet. This further limits the choice to a material having sufiicient strength and elasticity to resist the driving force on the bullet and the twisting force of the rifled barrel while holding the thickness T within reasonable allowances.

The relation between the various dimensions and variables can be determined by proper computation. I have found that the critical points are two. First: The modulus of elasticity of the material must be limited because of the requirement that the cup be opened by centrifugal force. The most practical clearance permitted should be about 1% of the diameter. However, the critical point is a minimum 4% of the diameter. The critical point may be met by any material having a modulus of elasticity equal or less than where:

V is the muzzle velocity in feet per second G is the specific gravity of the cup material R is the barrel twist in inches per one turn of rifling and C and B are dimensions as shown in FIG. 6.

This is a maximum allowable modulus :in terms of the specific gravity. Softer materials may be used so long as they satisfy the minimum shear strength requirement to prevent blowby or shearing of the cup past the bullet 11.

Again this shear strength may be readily computed. This also has a critical minimum value in pounds per square inch equal to in which equation B, L, T, C and H are dimensions of the cup in inches as shown in FIGURE 6, P is the effective breech pressure applied to the base of the first stage in pounds per square inch, D is the density of the material in grains per cubic inch and W is the weight of the bullet in grains. It will be recognized that in cases where no hole 13 is provided, the value of the dimension H becomes zero.

It is possible that under certain conditions of high breech pressures that a uniform material might not be found possessing all the requisite qualities. I therefore conceive of the possibility'of using a non uniform material. For example as illustrated in FIG. 8, a laminar material might be formed having a much denser lamination near the bottom 20 of the laminated cup 21. Such a cup could be punched or otherwise cut from a laminated sheet and formed from the blank so punched out.

Another possible alternative is a cup 22 (FIG. 7) fabricated from two different materials. In such a cup, the base 23 would be of a high shear, and compressive strength while the walls 24 would be more resilient. In such a cup, the walls 24 would be fastened to the base 23 by an adhesive. Since the base would be non-resilient, a small groove 25 would be required at the juncture of the base and walls to assure free movement of the bullet there from.

The same effect would be produced by the cup 27 shown in FIG. 9. Here the wall part 28 may be exactly like the walls 24 of the embodiment shown in FIG. 7. The base 29, however, may be made of a hard metal which is of a lesser diameter than the walls so that it will not damage the riding lands. The groove 25 is still needed for the same reason as with the device of FIG. 7.

In summary, my invention comprises a two stage bullet having a first stage of minimum sectional density consistent with accuracy holding a second stage having a high sectional density. The first stage is formed of a material of sufiicient strength to prevent rupture or shearing and of sufficient elasticity to allow the second stage to be released by the action of centrifugal force after the bullet passes the gun muzzle.

It is conceived that there may be variation within the stated specified devices. For example, the second stage may be a loose fit in the cup of the first stage and be held in place by the crimping of the cartridge case (not shown) about the cup. This type of device would require that the cup be pressed onto the bullet during firing by the rifling lands in the barrel. This is undesirable since it is less positive in its action and also because the bullet is harder to handle in its assembly into the cartridge. In my preferred device I use a light press fit between the bullet and the cup.

This results in an easier bullet to handle during assembly and a more sure grip between the two stages during passage through the barrel so that rotation is fully imparted to the bullet. This type of fit makes the use of the small hole 13 very desirable during assembly since the otherwise entrapped air can escape there through. This hole is further desirable because it provides an equalization of pressures between the base of the bullet and the base of the cup particularly at the moment of separation.

Having thus described my invention in its embodiment I am aware that further and extensive variations may be made therefrom without departing from the spirit and scope of my invention as limited only by the following claims.

I claim:

1. For firing from a gun having a rifled barrel, a two stage bullet comprising a cup-shaped first stage having walls and a base on said cup stage, and a bullet-shaped second stage, said walls being shaped to hold said second stage releasably in said first stage, said first stage being formed of an elastic material having an actual modulus of elasticity not greater than in which G is the specific gravity of the material, V is the muzzle velocity in feet per second, R is the lead in inchesper twist of the riiling, C is the outer diameter of the first stage in inches and B is the outer diameter of the second stage in inches, and said material having an actual shear strength in pounds per square inch not less than in which B and C are the same dimensions as in the equation for modulus of elasticity, L is the length of the first stage in inches, D is the density of the material in grains per cubic inch, W is the weight in grains of the second stage, T is the thickness of the base of the first stage in inches and P is the effective breech pressure at the base of the first stage in pounds per square inch.

2. The device of claim 1 in which the second stage is formed with an opening in said base, the equation for minimum shear strength being modified by substituting the term T(B -H for T B in the denominator where H is the diameter of said opening in inches.

3. The device of claim 1 in which the base is formed of a laminar material having composite strength at least equal to the minimum shear strength of the formula therefor and the walls of a different material having a modulus of elasticity of at most that described by the equation therefore.

4. The device of claim 3 in whiuh the base and walls are formed of separate materials joined together by an adhesive.

5. The device of claim 4 in which said walls are formed to provide a circumferential inner groove adjacent to said base.

6. The device of claim 4 in which the base is formed of a hard metal and has an outer diameter less than the outer diameter of said walls when compressed in said barrel.

7. The device of claim 5 in which said base is formed of a hard metal and has an outer diameter less than the guterl diameter of said walls when compressed in said arre I References Cited by the Examiner UNITED STATES PATENTS 384,574 6/88 Hawley 102-93 620,400 2/99 Ahrens 102-93 1,341,844 6/20 Dougan 102-93 2,663,259 12/53 Catlin et al. 102-93 X 2,820,412 1/58 Beeuwkes et a1 102-93 2,911,911 11/59 White 102-93 X 2,983,224 5/61 Prosen et al. 102-93 2,983,225 5/61 Walker 102-93 2,986,998 6/61 Clark 102-95 X 3,055,268 9/62 Rosenthal 102-93 X SAMUEL FEINBERG, Primary Examiner. 

1. FOR FIRING FROM A GUN HAVING A RIFLED BARREL, A TWO STAGE BULLET COMPRISING A CUP-SHAPED FIRST STAGE HAVING WALLS AND A BASE ON SAID CUP STAGE, AND A BULLET-SHAPED SECOND STAGE, SAID WALLS BEING SHAPED TO HOLD SAID SECOND STAGE RELEASABLY IN SAID FIRST STAGE, SAID FIRST STAGE BEING FORMED OF AN ELASTIC MATERIAL HAVING AN ACTUAL MODULUS OF ELASTICITY NOT GREATER THAN 